Document Type

Thesis - University Access Only

Award Date

2003

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

Donald M. Marshall

Abstract

Feed intake, monthly weights and carcass data were collected on 599 crossbred steers from 1989 to 2000 to estimate heritabilities for feed efficiency, residual feed intake, feed intake, average daily gain and various carcass traits. Genetic and phenotypic correlations were also estimated between feed intake, feed conversion ratio (measured as gain/feed) and residual feed intake ( another measure of feed efficiency) along with their correlations with the measured carcass traits. Heritability estimates and correlations were determined using MTDFREML (Boldman et al., 1995). Heritability estimates for feed intake and residual feed intake were 0.25 and 0.22 respectively. The heritability estimate for feed efficiency, measured as gain/feed, was 0.37, where as for the inverse of feed/gain the estimate was 0.17. Average daily gain was moderately heritable with an estimate of 0.36. Heritabilities of 0.29, 0.62, 0.58, 0.55, 0.20 and 0.36 were estimated for carcass weight, fat thickness, ribeye area, cutability, marbling and KPH, at an age-constant basis. At a constant empty body fat, heritability estimates for carcass weight, ribeye area, marbling and KPH were 0.45, 0.49, 0.26 and 0.44. Genetically and phenotypically, feed intake was positively correlated with residual feed intake and average daily gain (rg = 0.91, rp = 0.94 and rg = 0.49, rp = 0.32). The genetic correlation between feed intake and gain/feed was close to zero (r8 = -0.06) while phenotypically they were negatively correlated (rp = - 0.36). Gain/feed was positively correlated with average daily gain (r8 = 0.82 and rp = 0.76) and negatively correlated with residual feed intake (r8 = -0.49 and rp = -0.65). Both the genetic and phenotypic correlations between residual feed intake and average daily gain were close to zero (rg = 0.11 and rp = -0.02). Genetically, gain/feed was positively correlated with carcass weight and fat thickness (r8 = 0.52 and r8 = 0.43) and negatively correlated with ribeye area, cutability, marbling and KPH with estimates of -0.46, -0.52, - 0.14 and -0.32. Genetically, residual feed intake was positively correlated with ribeye area (0.53), cutability (0.54) and marbling (0.91) and negatively correlated with cwt (- 0.16), fat thickness (-0.06) and KPH (-0.23). Phenotypic correlations for gain/feed and residual feed intake with the carcass traits were near zero, except between gain/feed and carcass weight (rp = 0.70) and gain/feed and fat thickness (rp = 0.27). These results indicate genetic improvements in feed efficiency can be made through selection. Due to the correlated increases in carcass weight, average daily gain and fat thickness when selecting for gain/feed, residual feed intake may be a preferred measurement of feed efficiency.

Library of Congress Subject Headings

Beef cattle -- Feed utilization efficiency.
Beef cattle -- Genetics.
Heredity.
Beef cattle -- Feeding and feeds -- Effectiveness.

Publisher

South Dakota State University

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Rights Statement

In Copyright